US8218115B2 - Liquid crystal display device comprising a pixel electrode having a reverse taper shape with an edge portion that forms a transition nucleus in a liquid crystal layer - Google Patents

Liquid crystal display device comprising a pixel electrode having a reverse taper shape with an edge portion that forms a transition nucleus in a liquid crystal layer Download PDF

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Publication number
US8218115B2
US8218115B2 US12/211,964 US21196408A US8218115B2 US 8218115 B2 US8218115 B2 US 8218115B2 US 21196408 A US21196408 A US 21196408A US 8218115 B2 US8218115 B2 US 8218115B2
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Prior art keywords
liquid crystal
electrode
edge portion
transition
pixel electrode
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US12/211,964
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US20090079925A1 (en
Inventor
Yukio Kizaki
Rei Hasegawa
Yuko Kizu
Hirofumi Wakemoto
Kenji Nakao
Tetsuo Fukami
Tetsuya Kojima
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Toshiba Corp
Japan Display Central Inc
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Toshiba Corp
Toshiba Matsushita Display Technology Co Ltd
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Publication of US20090079925A1 publication Critical patent/US20090079925A1/en
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
    • G02F1/1393—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells
    • G02F1/1395—Optically compensated birefringence [OCB]- cells or PI- cells
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G02F1/133776—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers having structures locally influencing the alignment, e.g. unevenness
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1343—Electrodes
    • G02F1/134309—Electrodes characterised by their geometrical arrangement
    • G02F1/134336—Matrix

Definitions

  • the present invention relates to a liquid crystal display device having a display mode using birefringence.
  • the present invention relates to a liquid crystal display device having a display mode of forming a bend alignment in a liquid crystal material.
  • a liquid crystal display device having an optically compensated bend (OCB) mode has attracted interests.
  • OBC optically compensated bend
  • bend alignment is formed in a liquid crystal material, and a tilt angle of liquid crystal molecule is changed in the vicinity of each orientation film. In this way, retardation of a liquid crystal layer is changed.
  • liquid crystal material forms a splay alignment. This is because the splay alignment is inherently stable as compared with the bend alignment.
  • an operation for making a transition from the splay alignment to the bend alignment is required.
  • energy more than state energy difference between bend and splay alignments needs to be given.
  • voltage is applied to a liquid crystal cell, and thereby, given thereto in the form of electrostatic energy.
  • the progress of the foregoing transition is late; for this reason, very high voltage must be actually applied.
  • the transition progress is easy to receive an influence by a shape of a substrate surface or electric field distribution. As a result, a non-transferred area remains in the liquid crystal layer.
  • JP-A2003-280036 discloses the technique to solve the foregoing problem.
  • an insert-die shaped bend pattern hereinafter, referred to as transition nucleus forming portion
  • Potential difference is given between electrodes, and simultaneously, potential difference is given between counter electrodes.
  • heavy distortion of liquid crystal alignment is generated in the thickness and inner-face direction of the liquid crystal cell.
  • transition from splay alignment to bend alignment is made at high speed.
  • the foregoing Publication JP-A2003-280036 discloses a liquid crystal display device.
  • the transition nucleus forming portion is composed of a pixel electrode and a close electrode connected to a neighboring pixel electrode adjacent to the pixel electrode via a switching element. Potential difference equivalent to image signal amplitude is given between pixel electrodes, and simultaneously, potential difference is given between counter electrodes.
  • heavy liquid crystal alignment distortion is generated in the thickness direction and the in-plane direction of liquid crystal cell. A potential (voltage) change is prevented by capacitance coupling between the pixel electrode and a circumferential wiring to make a transition from a splay alignment to a bend alignment at high speed.
  • the transition nucleus forming portion is formed to be positioned just on a peripheral wiring electrode. Thus, numerical aperture and contrast can be kept higher.
  • a liquid crystal display device comprising:
  • a first substrate structure including a first insulating substrate, a first electrode, a second electrode arranged between the first insulating substrate and the first insulating substrate, and an insulating base layer disposed on the second electrode, on which the first electrode is formed, wherein the first electrode has a flat surface facing the third electrode and an edge portion which is a reverse taper shape gradually decreasing in its thickness toward the tip end;
  • a second substrate structure including a second insulating substrate, and a third electrode arranged on the second insulating substrate;
  • liquid crystal layer held between the first electrode and the third electrode, the liquid crystal layer being subject to a phase transition from a first state to a second state when an initialization voltage is applied to the first to third electrodes, the edge portion of the first electrode forming a transition nucleus in the liquid crystal layer based on application of the initialization voltage.
  • FIG. 1 is a top plan view schematically showing a liquid crystal display device according to one embodiment of the invention
  • FIG. 2 is a cross-sectional view showing the liquid crystal display device shown in FIG. 1 taken along the line II-II;
  • FIG. 3 is a cross-sectional view showing the liquid crystal display device shown in FIG. 1 taken along the line III-III;
  • FIG. 4 is an enlarged cross-sectional view showing the sectional structure of the liquid crystal display device shown in FIG. 1 taken along the line IV-IV;
  • FIG. 5 is a cross-sectional view schematically showing the structure of a counter electrode shown in FIG. 4 and its surrounding areas according to a modified embodiment
  • FIG. 6 is a cross-sectional view schematically showing the structure of a facing electrode shown in FIG. 4 and its surrounding areas according to another modified embodiment
  • FIG. 7 is a cross-sectional view schematically showing the structure of a counter electrode shown in FIG. 4 and its surrounding areas according to another modified embodiment
  • FIGS. 8A , 8 B and 8 C are schematic views sowing a manufacturing method according to the invention.
  • FIG. 9 is a cross-sectional view schematically showing the structure of a counter electrode and its surrounding areas according to a comparison example of the invention.
  • a liquid crystal display device according to one embodiment of the invention will be hereinafter described with reference to the accompanying drawings.
  • the same reference numerals are used to designate the constituent components having the same or similar function, and the details are omitted.
  • FIG. 1 is a top plan view schematically showing a liquid crystal display device according to the invention.
  • FIG. 2 is a cross-sectional view showing the liquid crystal display device taken along the line II-II shown in FIG. 1 .
  • FIG. 3 is a cross-sectional view showing the liquid crystal display device taken along the line III-III shown in FIG. 1 .
  • a color filter described later is not illustrated.
  • the liquid crystal display device is an OCB mode active matrix type liquid crystal display device.
  • the OCB mode active matrix type liquid crystal display device includes a liquid crystal panel 1 and a back light (not shown) arranged facing the liquid crystal display panel 1 .
  • the liquid crystal display device further includes a scanning line driver (not shown) and a signal line driver (not shown) for driving the liquid crystal display panel 1 .
  • a liquid crystal display panel 1 includes an array substrate, that is, a backside substrate 10 and a front substrate 20 .
  • the front substrate 20 is used as a substrate facing the backside substrate 10 .
  • a frame-like bonding agent layer (not shown) is interposed between the backside substrate 10 and the front substrate 20 .
  • a gap is formed between the backside substrate 10 and the front substrate 20 .
  • the gap formed between the backside substrate 10 and the front substrate 20 that is, a gap surrounded by the bonding agent layer is filled with a liquid crystal material.
  • the liquid crystal material forms a liquid crystal layer 30 .
  • an optical compensation film 40 and a polarizer 50 are successively stacked on the outer surface of the backside substrate 10 and the front substrate 20 .
  • the backside substrate 10 comprises a transparent substrate 100 such as glass substrate, for example.
  • An under coat layer 101 such as SiNx layer and/or SiO 2 layer is formed on the transparent substrate 100 .
  • a semiconductor layer 102 such as polysilicon layer formed with a channel and source/drain is provided on the under coat layer 101 .
  • the semiconductor layer 102 and the under coat layer 101 is covered with a gate insulating film 103 .
  • the gate insulating film 103 is formed using tetraethoxyorthosilane (TEOS).
  • a scanning line shown in FIG. 1 and FIG. 3 , a gate electrode shown in FIG. 1 and FIG. 2 and a reference wiring 106 shown in FIG. 1 and FIG. 3 are arranged in parallel.
  • the scanning line 104 is extended to a first direction, and arrayed along a second direction crossing the first direction.
  • the scanning line extends to the horizontal or X direction equivalent to a row direction and is arrayed in a Y direction equivalent to the longitudinal or column direction.
  • a metal material is usable as the scanning line 104 .
  • MoW is usable as the material of the scanning line 104 .
  • the scanning line 104 is connected to a scanning line driver (not shown), and driven according to a scan signal supplied from the scanning line driver.
  • the thin film transistor is given as the switching element 110 .
  • other elements such as a diode or metal-insulator-metal (MIM) may be used.
  • the reference wiring 106 is extended to the X direction, and arrayed in the Y direction crossing the X direction. In this case, one reference wiring 106 is provided every the scanning line 104 .
  • Metal material is usable as the reference wiring 106 ; for example, MoW is usable.
  • the reference wiring 106 is formable in the same process as the scanning line 104 .
  • the signal line 108 is extended to the second direction, and arrayed in the first direction.
  • the signal line 108 is extended to the Y direction, and arrayed in the X direction.
  • a metal material is usable as the signal line 108 .
  • the signal line 108 can employ a three-layer structure of Mo layer, Al—Nd layer and Mo layer.
  • the signal line 108 is connected to a signal line driver (not shown), and an image signal from the signal driver is supplied to the signal line 108 .
  • the thin film transistor is used as the switching element 110 , and as shown in FIG. 2 , the signal line 108 is connected to the drain of the thin film transistor via a through hole formed in the interlayer insulating film 107 .
  • the signal line 108 is used as the drain electrode.
  • one terminal of the drain electrode 109 is connected to the source of a thin film transistor 110 via a through hole formed in the interlayer insulating film 107 .
  • the other terminal of the drain electrode 109 is formed in an electrode area facing the reference wiring 106 via the interlayer insulating film 107 as shown in FIG. 1 and FIG. 3 .
  • the drain electrode 109 , the reference wiring 106 and the interlayer insulating film form a capacitor.
  • the same material as the signal line is usable for the drain electrode 109 .
  • the foregoing interlayer insulating film 107 , signal line 108 and drain electrode 109 are covered with an insulating base layer or foundation layer 112 .
  • the insulating base layer 112 may be formed of at least one of a passivation film 111 or a color filter 120 .
  • the passivation film 111 covers the interlayer insulating film 107 , the signal line 108 and the drain electrode 109 as seen from FIG. 2 and FIG. 3 .
  • SiNx, transparent acrylate resin, benzocyclobutane (BCB), photosensitive polyimide and epoxy resin are usable as the passivation film 111 .
  • the transparent acrylate resin is preferable on patterning characteristic and cost.
  • the color filter is composed of a plurality of colored layers having different absorption spectrum, for example, green colored layer G, blue colored layer B and red colored layer R. These colored layers G, B and R have a band shape extending to the Y direction as seen from FIG. 3 . These colored layers are arrayed along the X direction to form a stripe pattern. As shown in FIG. 2 , the boundary between the colored layers G, B and R is arranged to be positioned on the signal line 108 . For example, mixture of transparent resin and dye and/or pigment is usable as the colored layers G, B and R.
  • the color filter 120 is provided in the backside substrate 10 .
  • the color filter 120 may be provided in the front substrate 20 .
  • a pixel electrode 130 is arrayed on the color filter 120 to correspond to the thin film transistor 110 .
  • the pixel electrode comprises indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide doped with antimony and fluorine or a transparent conductor such as organic conductive polymer.
  • ITO indium tin oxide
  • IZO indium zinc oxide
  • tin oxide doped with antimony and fluorine or a transparent conductor such as organic conductive polymer These pixel electrodes 130 are connected to the drain electrode 109 via the passivation film 111 and the through hole formed in the color filter 120 as seen from FIG. 1 to FIG. 3 .
  • the pixel electrode 130 and the color filter 120 are covered with an orientation film 140 .
  • a resin such as polyimide is usable as the material for the orientation film 140 .
  • a rubbing alignment layer treatment is carried out with respect to the orientation film 140 . According to the alignment treatment, a rise angle of liquid crystal molecule 300 on a film surface is determined; for example, rubbing treatment is selected. If the rubbing treatment is carried out as the alignment treatment, in FIG. 1 , an angle shown by an arrow is set as a rubbing angle.
  • the pixel electrode 130 is formed to have a rectangular shape extending to the Y direction.
  • the end portion of the pixel electrode 130 is formed with a transition nucleus forming portion 131 in the Y direction.
  • the transition nucleus forming portion 131 is equivalent to a boundary area contacting with a neighboring pixel electrode 130 in the Y direction, and formed to overlap with the drain electrode 109 .
  • the shape of the transition nucleus forming portion may be a bend pattern crossing a rubbing angle.
  • a comb teeth pattern, a combination of different shape pattern or a chain pattern may be employed.
  • FIG. 1 there is shown a continuous square pattern crossing the rubbing angle at an angle of 45°.
  • FIG. 4 is an enlarged cross-sectional view taken along the line IV-IV shown in FIG. 1 .
  • the transition nucleus forming portion 131 on the pixel electrode 130 is formed into a reverse taper shape. Specifically, the upper surface of the pixel electrode 130 facing the liquid crystal layer 30 is kept flat, and the edge portion thereof is made thin gradually toward the tip end in its thickness. An edge-shaped space is formed between the edge portion of the pixel electrode 130 and the insulating base layer 112 . Liquid crystal of the liquid crystal layer 30 comes into the edge-shaped space.
  • An edge angle ⁇ is set to 10 degrees or more and 60 degrees or less.
  • the pixel electrode 130 is formed to have a thickness of 500 ⁇ to 5000 ⁇ considering a range suitable to transmittance and a resistance value.
  • the thickest portion on the center portion is defined as the thickness TO of the pixel electrode 130 , and not the edge portion.
  • a taper length LT is calculated from a trigonometric function based on the thickness of the pixel electrode 130 and a range of the edge angle ⁇ . As a result, the taper length LT is set to 290 ⁇ to 28000 ⁇ . If the taper length LT is short, the edge-shaped space formed between the edge portion of the pixel electrode 130 and the insulating base layer 112 becomes small.
  • the taper length LT is long, it is difficult to form a taper shape, and thus, this is a factor of increasing the cost.
  • a preferable range of the taper length LT is 1000 ⁇ to 5000 ⁇ .
  • the color filter 120 is provided on the front substrate 20 , and not the backside substrate 10 , and the pixel electrode 130 is formed on the insulating base layer 112 .
  • a patterning process such as gray scale exposure process and lift-off process using a positive-negative invert resist is selected as the method of forming the edge portion of the transition nucleus forming portion into a reverse taper.
  • One example of the formation process is schematically showing in FIG. 8A to FIG. 8C .
  • a resist 301 is coated on the insulating base layer 112 , and the resist 301 is formed so that a part of the resist 301 has a stepped shape via a gray scale exposure process.
  • a pixel electrode 130 is deposited. Thereafter, as seen from FIG.
  • the resist is solved and removed via a lift-off process so that a part of the pixel electrode 130 is formed into a reverse taper shape.
  • adhesion of the pixel electrode 130 and the insulating base layer 112 is optimized.
  • the pixel electrode 130 is formed into a desired reverse taper shape by side etching effect in an etching process.
  • a portion 132 having no pixel electrode 130 on the insulating base layer 112 may be formed into a thin stepped shape via 02 ashing and UV/03 dry cleaning treatment.
  • the front substrate 20 comprises a transparent substrate 200 such as glass substrate, for example.
  • the substrate 200 is arranged to face the surface where an orientation film 140 of the backside substrate 10 is formed.
  • the facing surface of the substrate 200 facing the backside substrate 10 is formed with a common electrode 230 used as a counter electrode.
  • a common electrode 230 used as a counter electrode.
  • ITO indium tin oxide
  • IZO indium zinc oxide
  • tin oxide doped with antimony oxide and fluorine or a transparent conductor such as organic conductive polymer are usable as the common electrode 230 .
  • the common electrode 230 is covered with an orientation film 240 .
  • the orientation film 240 is arranged separating from the orientation film 140 positioned on the pixel electrode 130 via a spacer (not shown).
  • a resin such as polyimide is usable as the material for the orientation film 240 .
  • An alignment treatment such as rubbing is carried out with respect to the orientation film 240 .
  • An alignment treatment of determining a rise direction of liquid crystal molecule 300 in the film surface, for example, rubbing treatment is selected. If the rubbing treatment is carried out as the alignment treatment, the direction shown by the arrow in FIG. 1 is set as a rubbing direction.
  • a frame-like bonding agent layer (not shown) is interposed between the backside substrate 10 and the front substrate 20 .
  • Particle spacers are interposed inside the frame formed with the bonding agent layer between the backside substrate 10 and the front substrate 20 .
  • the facing surface of at least one of the backside substrate 10 and the front substrate 20 is formed with a pillar spacer. These spacers perform a function of keeping constant the thickness of the space surrounded by the backside substrate 10 , the front substrate 20 and the bonding layer.
  • the liquid crystal layer 30 is formed of a liquid crystal material, which is positive in dielectric anisotropy and refractive anisotropy. While, voltage is applied between the pixel electrode 130 and the common electrode 230 , the liquid crystal material forms a bend alignment. Typically, a switch is made between a first value that the absolute value of voltage applied between the pixel electrode 130 and the common electrode 230 is larger than zero and a second value larger than the first value. In this way, brightness display and dark display are switched. According to this embodiment, the first value may be zero; therefore, the first value includes zero.
  • a state that the absolute value of the applied voltage is set as the first value calls an off state
  • a state that the absolute value of the applied voltage is set as the second value calls an on state.
  • FIG. 2 and FIG. 3 arrangement of the liquid crystal molecule 300 forming a bend alignment is illustrated as a 45° projection image to paper.
  • the tilt angle of the liquid crystal molecule in the vicinity of the orientation films 140 and 240 becomes large as compared with the off state.
  • the optical compensation film 40 comprises a biaxial film, for example.
  • the optical compensation film 40 includes a uniaxial compound having negative refractive anisotropy, for example, an optical anisotropic layer formed in such a manner that a discotic liquid crystal compound is hybrid-aligned.
  • An optical axis of the uniaxial compound included in the optical compensation film 40 on the substrate 100 is approximately parallel with an optical axis in the on state of the liquid crystal molecule 300 positioned near the backside substrate 10 on the side of the substrate 100 .
  • the foregoing optical axis is approximately parallel with an optical axis in the on state of the liquid crystal molecule 300 positioned at the intermediate portion between the backside substrate 10 and the front substrate 20 .
  • An optical axis of the uniaxial compound included in the optical compensation film 40 on the substrate 200 is approximately parallel with an optical axis in the on state of the liquid crystal molecule 300 positioned near the front substrate 20 on the side of the substrate 200 .
  • the foregoing optical axis is approximately parallel with an optical axis in the on state of the liquid crystal molecule 300 positioned at the intermediate portion between the backside substrate 10 and the front substrate 20 .
  • the sum of retardation of these optical compensation filters 40 is set to an approximately equal value of retardation in the on state of the liquid crystal layer 300 .
  • the polarizer 50 is arranged so that the transmission axis is mutually perpendicular. Each polarizer 50 is arranged so that the transmission axis is made at an angle of about 45° to the X and Y directions.
  • a backlight (not shown) is arranged to illuminate the backside substrate 10 of the liquid crystal display panel 1 .
  • voltage is applied to the pixel electrode 130 , the common electrode 230 and the reference wiring 106 from an initialization voltage source 60 , as shown in FIG. 4 .
  • a first AC voltage of ⁇ 5V is applied to the pixel electrode 130 from the initialization voltage source 60 .
  • a second AC voltage of ⁇ 15V is applied to the common electrode 230 in a phase reverse to the first AC voltage.
  • the reference wiring 106 is kept to a third voltage of 0V. Therefore, in the liquid crystal layer 30 , a vertically electric field is formed between the pixel electrode 130 and the common electrode 230 . In addition, a horizontally electric field is formed between the pixel electrode 130 the reference wiring 106 .
  • a transition nucleus is formed in the vicinity of the transition nucleus forming portion in the liquid crystal layer 30 of each pixel by the foregoing electric fields. Liquid crystal is rapidly transferred from a splay alignment state to a bend alignment state. Thereafter, an image signal is supplied to the signal line 108 , and further, a scanning signal is supplied to the scanning line 104 so that an image is displayed on the liquid crystal panel 1 .
  • the structure of a normally white drive liquid crystal panel 1 is described.
  • the liquid crystal panel 1 may be designed to make a normally block drive.
  • the configuration of compensating the on state is employed.
  • the configuration of compensating the off state may be employed.
  • the embodiment of the invention has the following structure. Specifically, the edge portion of transition nucleus forming portion 131 is formed into a reverse taper shape while the surface facing the liquid crystal layer 30 is kept flat. Namely, the transition nucleus forming portion 131 is gradually made thin toward the tip end. Thus, the field strength by the shape of the electrode is not uniform in the transition nucleus forming portion provided in the pixel electrode 130 .
  • An alignment state of the liquid crystal molecule 300 near the reverse taper electrode is easy to become unstable as compared with a bulk alignment state of the liquid crystal layer 30 . For this reason, it is easy to form alignment distortion. As a result, it is possible to perform high-seed transition from a splay alignment to a bend alignment of all pixels.
  • FIG. 1 to FIG. 5 there is shown the structure in which the transition nucleus forming portion 131 is provided around the pixel.
  • the transition nucleus forming portion 131 may be provided in an opening in the pixel.
  • FIG. 1 to FIG. 5 shows an active matrix liquid crystal display device.
  • other drive type such as a simple matrix may be employed as the liquid crystal display device.
  • the drive type of the liquid crystal display device is not specially limited.
  • a liquid crystal display device according to various embodiments of the invention will be hereinafter described.
  • the OCB mode liquid crystal display device shown in FIG. 1 to FIG. 5 was manufactured using the following method.
  • the outer surface of the backside substrate 10 was not provided with the optical compensation film 40 .
  • the outer surface only of the front substrate 20 was not provided with the optical compensation film 40 .
  • the structure from an under coat layer 101 to the pixel electrode 130 was deposited on a glass substrate 100 having a thickness of 0.5 mm, and then, formed via a photolithography process.
  • indium tin oxide (ITO) was used as the pixel electrode 130
  • MoW was used as a reference wiring 106
  • a transparent acrylate resin was used as an insulating base layer 112 .
  • a common electrode 230 was formed on a glass substrate 200 having a thickness of 0.5 mm.
  • the pixel electrode had a rectangular shape, and the pitch in the X direction was set to 82 ⁇ m while the pitch in the Y direction was set to 246 ⁇ m.
  • Resist patterning was carried out using a SU-8 resist made by Microchem company via a gray scale exposure process. Then, indium tin oxide (ITO) was deposited as the pixel electrode 130 having a thickness 1000 ⁇ via sputtering, and thereafter, lifted off. As shown in FIG. 4 , the edge portion of a transition nucleus pattern of the pixel electrode was formed into a reverse taper, and the edge angle ⁇ was 30 degrees.
  • ITO indium tin oxide
  • An optoma-AL 3456 made by JSR Kabushiki Kaisha was coated on the pixel electrode 130 and the common electrode 230 via spin coating to form a polyimide resin layer having a thickness of 0.1 ⁇ m. A rubbing treatment was carried out with respect to each polyimide resin layer along the direction shown in FIG. 1 . In this way, orientation film 140 and 240 were obtained.
  • thermosetting bonding agent was dispensed on the main surface of the backside substrate 10 to surround the orientation film 140 .
  • a frame formed by the bonding agent was formed with an opening used as a liquid crystal injection inlet.
  • the bonding agent was temporarily dried, and thereafter, a silver paste was dispensed on a transfer pad (not shown).
  • particle spacers having a diameter of 7.0 ⁇ m were sprayed on the orientation film 240 .
  • the particle spacer was sprayed as the spacer; however, in place of the particle spacer, a pillar spacer may be formed using a photosensitive resin.
  • a nematic liquid crystal compound having positive dielectric anisotropy was injected to the free cell via a dip process.
  • an ultraviolet thermosetting resin was dispensed to the liquid crystal injection inlet, and thereafter, ultraviolet rays were irradiated thereto.
  • a polarizer 50 was bonded to the outer surface of the backside substrate 10 , and an optical compensation film 40 and a polarizer 50 were successively bonded to the outer surface of the front substrate 20 .
  • the optical compensation film 40 used herein includes the following optical anisotropy layer. According to the optical anisotropy layer, a bend alignment is formed so that an optical axis of a discotic liquid crystal compound changes in in-plane vertical to the X direction.
  • the maximum main normal speed direction of the optical compensation film 40 is parallel with the thickness direction.
  • the minimum main normal speed direction of the optical compensation film 40 is parallel with the X direction.
  • the remaining main normal speed direction is parallel with the Y direction.
  • the liquid crystal display panel 1 thus obtained was incorporated into a backlight unit (not shown), and thereby, the liquid crystal display device shown in FIG. 1 to FIG. 4 was manufactured.
  • the liquid crystal display device was observed in the following condition. Specifically, AC voltage of ⁇ 5V was applied; inversion-phase AC voltage of ⁇ 15V was applied to the common electrode 230 , and 0V was applied to the reference wiring 106 under room temperature and in a state that the backlight was lighted. In this way, the pixel was observed using a microscope. As a result, an average time required for a change from a colored state showing a splay alignment to a non-colored state showing a bend alignment was 0.10 second per pixel. Via repeating measurements, an average spent time until color change is completed on the entire screen was 0.20 seconds.
  • a liquid crystal display device shown in FIG. 1 to FIG. 3 and FIG. 6 was manufactured.
  • the reverse taper was formed into a step shape.
  • the pixel was observed using a microscope under room temperature and in a state that the backlight is lighted.
  • an average time required for a change from a colored state showing a splay alignment to a non-colored state showing a bend alignment was 0.15 second per pixel.
  • an average spent time until color change is completed on the entire screen was 0.25 seconds.
  • an organic conductive polymer transparent electrode having a thickness of 2000 ⁇ was formed in the following manner. Specifically, the pixel electrode 130 was converted to a tin oxide of a conductive metal oxide in a manner that tin chloride is heated using a solution containing hydroxypropyl cellulose as organic polymer component and tin oxide as inorganic sol component. Resist patterning was carried out using an AZP 4903 resist made by Clariant Japan company, and etching was carried out using hydrochloric/nitric acid etching solution. As seen from FIG. 6 , the edge portion of the transition nucleus forming portion of the pixel electrode 130 was formed into a reverse taper shape.
  • the pixel electrode 130 was formed into a step shape toward the tip end so that the thickness is decreased.
  • An edge angle ⁇ was 40 degrees.
  • a portion of the insulating base layer 112 where the pixel electrode 130 is not formed was formed into a step shape because the thickness is made thin via 02 ashing treatment.
  • transition spent time from a splay alignment state to a bend alignment state was measured according to the same method as carried out in the embodiment 1.
  • an average transition spent time per pixel was 0.08 second.
  • an average spent time until color change is completed on the entire screen was 0.15 seconds.
  • a transparent acrylate resin was used as the insulating base layer 112 .
  • the insulating base layer having a thickness of 1.5 ⁇ m was formed, and thereafter, a hydrophilicity treatment was carried out with respect to the surface using titanium oxide photo catalyst.
  • the pixel electrode 130 was formed in the following manner. Specifically, indium zinc oxide (IZO) was deposited to have a thickness of 1500 ⁇ via sputtering. Thereafter, resist patterning was carried out via normal exposure process using an AZP 4903 resist made by Clariant Japan company. Then, etching was carried out using hydrochloric/nitric acid etching solution.
  • IZO indium zinc oxide
  • the hydrophilicity treatment was previously carried out with respect to the insulating base layer 112 , and thereby, surface energy on the surface changed.
  • the edge portion of the transition nucleus pattern of the pixel electrode 130 was formed into a reverse taper shape by the effect of facilitating sink of the hydrochloric/nitric acid etching solution.
  • An edge angle was 35 degrees.
  • a portion of the insulating base layer 112 where the pixel electrode 130 was not formed is made thin via 02 ashing treatment; as a result, a step shape was obtained.
  • transition spent time from a splay alignment state to a bend alignment state was measured according to the same method as carried out in the embodiment 1.
  • an average transition spent time per pixel was 0.05 second.
  • an average spent time until color change is completed on the entire screen was 0.10 seconds.
  • the pixel electrode 130 was formed in the following manner. Specifically, an indium tin oxide (ITO) was deposited to have a thickness of 1000 ⁇ via sputtering, and thereafter, resist patterning was carried out using a TSMR-V90 resist made by Tokyo Oka Kogyo company. Then, the resultant indium tin oxide (ITO) was etched using dry etching. As seen from the edge portion of a transition nucleus pattern of the pixel electrode 130 was formed into an approximately vertical shape.
  • ITO indium tin oxide
  • transition spent time from a splay alignment state to a bend alignment state was measured according to the same method as carried out in the embodiment 1. As a result, an average transition spent time per pixel was 0.5 second. An average spent time until transition is completed on the entire screen was 0.8 seconds.
  • each configuration of element and drive circuit is simplified, and it is possible to easily perform transition from a splay alignment to a bend alignment in all pixels.
  • numerical aperture and contrast can be improved.
  • liquid crystal display device which has simple element and drive circuit configuration, and performs transition from a splay alignment to a bend alignment in all pixels, and further, improves numerical aperture and contrast.

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US12/211,964 2007-09-26 2008-09-17 Liquid crystal display device comprising a pixel electrode having a reverse taper shape with an edge portion that forms a transition nucleus in a liquid crystal layer Expired - Fee Related US8218115B2 (en)

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JP6202370B2 (ja) * 2013-05-31 2017-09-27 大日本印刷株式会社 タッチパネルセンサ、タッチパネルセンサを備える入出力装置およびタッチパネルセンサの製造方法
CN106094379A (zh) * 2016-08-17 2016-11-09 深圳市华星光电技术有限公司 一种显示面板及其阵列基板
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US20050190322A1 (en) * 2004-02-25 2005-09-01 Satoshi Okabe Etching composition for laminated film including reflective electrode and method for forming laminated wiring structure
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